A case of monkeypox, a rare but potentially serious viral illness, has been identified in a Texas resident who recently returned from Nigeria, health officials said on Friday. They said that the risk that the virus would spread to others was low.
The patient, a Dallas resident, was hospitalized in Dallas and in stable condition, health officials said.
The Centers for Disease Control and Prevention said it was working with an unidentified airline as well as state and local health officials to contact passengers who had traveled with the patient on two flights — one from Lagos to Atlanta on July 8 and the other from Atlanta to Dallas on July 9.
The C.D.C. said it believed that the risk of the patient’s having spread monkeypox to others through respiratory droplets was limited because travelers on those flights and in the airports in Atlanta and Dallas were required to wear masks to prevent the spread of the coronavirus.
“While rare, this case is not a reason for alarm, and we do not expect any threat to the general public,” Clay Jenkins, the Dallas County judge, said in a statement on Friday.
Dr. Philip Huang, the director of Dallas County Health and Human Services, said that county health officials had been working with state and federal agencies to interview the patient and others who had been in close contact with the person.
“We have determined that there is very little risk to the general public,” Dr. Huang said in a statement. “This is another demonstration of the importance of maintaining a strong public health infrastructure, as we are only a plane ride away from any global infectious disease.”
Monkeypox — so named because it was first identified in laboratory monkeys — occurs mostly in Central and Western Africa, although it caused an outbreak in the United States in 2003 after it spread from imported African rodents to pet prairie dogs, the C.D.C. said.
During that outbreak, 47 confirmed and probable cases of monkeypox were identified in six states, the C.D.C. said. Those who were infected reported symptoms such as fever, headache, muscle aches and rash. No deaths were reported.
Monkeypox is in the same family of viruses as smallpox, but it causes a milder infection, according to the C.D.C. The illness typically begins with flulike symptoms and swelling of the lymph nodes and develops into a widespread rash on the face and body. Most infections last two to four weeks.
In this case, laboratory testing at the C.D.C. showed that the patient had been infected with a strain of monkeypox most commonly seen in parts of West Africa, including Nigeria. Infections with that strain of monkeypox are fatal in about 1 in 100 people, the C.D.C. said, although rates may be higher in people with weakened immune systems.
The C.D.C. said it had been supporting Nigeria’s response to monkeypox since 2017, when the disease re-emerged in that country after a period of nearly 40 years with no reported cases.
There are no specific treatments available for monkeypox infection, according to the C.D.C., although one vaccine has been licensed in the U.S. to prevent monkeypox and smallpox.
Monkeypox is commonly found in animals such as rats, mice and rabbits, but it can infect people when they are bitten or scratched by an animal, prepare wild game or come into contact with an infected animal or, possibly, animal products, the C.D.C. said.
The virus can spread between people through bodily fluids, sores or items contaminated with bodily fluids, but it is generally transmitted through large respiratory droplets that do not travel more than a few feet. As such, prolonged face-to-face contact is generally necessary for the virus to spread, the C.D.C. said.
Dr. Anne W. Rimoin, a professor of epidemiology at the U.C.L.A. Fielding School of Public Health, said that monkeypox was not as transmissible as coronavirus or influenza.
“The risk is low, but this just highlights the fact that an infection anywhere is potentially an infection everywhere,” Dr. Rimoin said. “This should serve as a reminder that infectious diseases are spilling from animals to humans regularly and that Covid is not the only infectious disease of zoonotic origin that we may worry about in the future.”